Emergency department / hospital crowding is a major public health problem that leads to degradation in both process and outcome measures in a variety of conditions (eg, acute cardiac care, care for the elderly, pneumonia, pain management, pediatric care, and public health screening). The crowding problem has shown "policy resistance";despite being a source of concern for 20 years, it continues worsen, and many current proposals have feedbacks that exacerbate the problem in a vicious cycle. Because of its dynamic complexity, delayed feedback loops, and social-behavioral components, the problem is ideally suited to a system dynamics approach. For example, a system dynamics understanding of crowding would be useful in: " Developing early warning capabilities of a potential overcrowding crisis " Identifying leverage points for managing dynamic and unexpected changes in patient demand or organizational capacity to respond" Identifying potentially dysfunctional interventions to be avoided, ie, that might provide short term relief but ultimately make the overall problem worse. The broad, overall objective of this project is use a systems science approach, specifically system dynamics modeling, to study the problem of emergency department (ED) and hospital crowding in order to inform departmental, organizational, regional, and societal policies and interventions aimed at alleviating it. The project will engage a team of organizational stakeholders and system science experts to construct system dynamic models of the ED / hospital crowding problem, based on data and experience at a single healthcare organization that has experienced severe crowding problems. These models will focus on ordinary operations, i.e., not external disaster scenarios. We will then use the models for exploration and experimentation to identify characteristic behaviors, evaluate potential interventions, and identify leverage points and critical variables supporting resilient performance. The models will use acute cardiac care and care for the elderly as specific 'tracers'to evaluate performance. Acute cardiac care is ideal for this role, because it is serious, depends on high quality emergency care for optimal results, is sensitive to degradation due to crowding, is of great public health interest, is central to the mission of emergency care workers and health care organizations, and has good process and outcome measures. Another potential tracer condition is care for the elderly, who are disproportionately affected by ED / hospital crowding in several ways (e.g., impaired access to care in crowding situations, 'boarding'in hallways or other non-standard care spaces, and premature discharge from the hospital to make room for new admissions). It would thus be most suitable for the NHLBI as primary funder, and for the NIA as secondary. PUBLIC HEALTH RELEVANCE: ED - hospital crowding affects roughly 110 million Americans per year, and is associated with decreased quality of care and increased morbidity and mortality. Crowding has been increasing over the past 2 decades, despite many efforts to control it. This project will apply a new method to the study of crowding to inform management and policy by better identifying leverage points, and characterizing potentially useful and potentially counterproductive interventions.